IMHO quite generous by them, in my former companies you skipped the raise talk if you joined less than 9 months ago. Makes sense, because you just negotiated your salary on entry.

> Makes sense, because you just negotiated your salary on entry.

Not really, as in this field that is about halfway through your tenure. Market has certainly shifted a lot in 9 months past.

18 month tenure seems short, even for IT employees. Better off just staffing with contractors if that's truly expected.

Devs seem to last two years, but they make the decision to leave well before that, so you need to get a retention offer in before they start the job search.

Any data on that?

Only anecdotal, but that seems to be how long people last. There are no devs that I knew at either of my past two jobs that remain. Virtually all friends report similar experiences.

My experience goes the other way. 75%+ have been at my company for 5+ years.

Inventing arbitrary formulae to calculate your wage is merely a dishonest negotiation tactic. Govt companies do it all the time, don't read too much into it. Also, it's perfectly fine to renegotiate your wage once you're off your probation period, as once you're in, you have a better idea of your worth to the company. Just don't do it too often.